From DE 195 27 912 A1 a drive acting on both sides is known wherein the drive lever is mounted on a drive axle and supports swivel locking elements whose free ends are provided with toothed elements that can be brought into engagement with the gearing mounted on the circumference of a drive wheel. A slide guide is associated with the swivel locking elements and lifts the relevant unloaded locking element away from the gearing of the drive wheel depending on the swivel direction of the drive lever. Spring areas are thereby provided both sides and outside the slide guide to exert on the locking elements a force which is directed against the engagement direction of the teeth whereby so-called ratchet noises are avoided.
In one embodiment the gearing provided on the circumference of the drive wheel has internal teeth and the locking elements are mounted on an axis of the drive lever inside the circumference formed by the internal teeth.
One disadvantage with the adjustment drives known from DE 195 27 912 A1 is, on the one hand, the relatively large number of parts. More particularly two independent locking elements are required for an adjustment acting on both sides. This also entails a correspondingly large structural space for the adjustment drive. On the other hand a relatively expensive construction is required in order to provide a defined guide for the locking elements and to avoid the teeth of the locking elements catching on the teeth of the drive wheel as the drive lever is returned to the neutral position. JP A 05176819 describes an adjustment mechanism for adjusting the incline of the seat back of a vehicle seat wherein on operating an operating lever an unlocking action occurs and free adjustment of the incline of the seat back can then be carried out. On releasing the operating lever renewed locking occurs. For locking, two locking parts coupled to the operating lever and mounted rotatable on a spindle are provided with toothed areas which can be brought into engagement with counter teeth and can be brought out of and into engagement with the counter teeth by operating and releasing the operating lever accordingly.